Generally, the aqueous urea solution is stored in a dedicated tank in the vehicle, which is connected to the selective catalytic reduction system of said vehicle.
In the present invention, the terms “selective catalytic reduction system” mean a system comprising a tank of an aqueous urea solution, a catalyst, an injector of the aqueous urea solution in the exhaust line and at least one pipe connecting the tank to the injector, the catalyst being positioned at the exhaust line downstream of the inlet of the injector so that the catalysis occurs on a mixture of exhaust gas circulating in the exhaust line and of aqueous urea solution injected upstream of the catalyst in said exhaust line.
In a known manner, the aqueous urea solution contained in a storage device of a vehicle tends to freeze around −11° C. Therefore, the aqueous urea solution storage device is generally equipped with a system for heating said solution in order to prevent the latter from freezing.
There are several types of aqueous urea solution heaters. For example, preferentially for heavy goods vehicles, the calories of the engine cooling system are used by means of a stainless steel plunger used as a heat exchanger immersed in the tank. This solution is not yet adopted for light motor vehicles to the extent that the aqueous urea solution tank is located opposite the engine cooling system, which requires piping of considerable length traversing the entire vehicle and consequently cumbersome piping. In addition, making stainless-steel plungers is expensive and complicated.
In addition, there are also heating devices comprising one or more heating member(s), such as resistive tracks or thermistors with a positive temperature coefficient called PTC in the following application, equipped or not with an aluminum heat diffuser for example, the whole being overmolded by a compatible material for an immersion in the aqueous urea solution, such as silicone, polyoxymethylene (POM) or high-density polyethylene (HDPE). These overmolded devices have several drawbacks. Plastic, generally thermoplastic, materials used for the overmolding have generally relatively low melt temperatures, which causes a limitation of the power density of the devices to prevent the overmolding from melting, which leads to an increase in the exchange surfaces and therefore to a high bulk. In addition, the plastic materials used are generally poor heat conductors, which reduces the efficiency of the heaters. Finally, these plastic materials having a coefficient of expansion different from the resistive tracks or diffusers, there is a significant risk of occurrence of cracks, breaks or detachment of the overmolding, thereby making the heater inefficient or even ineffective.